Fin tubing



Feb. 26, 1935. E. A. DEWALD FIN TUBING- Filed March 6, 1933 2Sheets-Sheet l w gv H15 ATTORNEYS Patented Feb. 26, 1935 FIN TUBINGEdward A. Dewald, Massillon, Ohio, assignor, by mesne assignments,toReconstruction Finance Corporation, a corporation of the United StatesApplication March 6, 1933, Serial No. 659,892 3 Claims. (01. 257-262)yThis invention relates to fin tubing and more particularly concerns animproved finned tube having novel means for securing the fin to the tubesurface, as well as an improved method of producing this tube.

Fin tubing of the type concerned herein comprises a metallic tube havingsecured to the external surface thereof a thin ribbon-like metallic finin the form of a helix. Fin tubing of this nature is extensively used inthe manufacture of heat exchangers.

In the past, fin tubing of the character described has been made ineither one of two different ways. Thus, the thin ribbon or strip ofmetallic fin material has been wound helically on a tube and thensecured thereto by a molten metal bond of solder or the like. It hasalso been the practice to cut a helical groove on the outer surface ofthe tube, insert the inner edge of a helical fin in such groove andpress the edges of the groove into clamping relation with the fin edgeso inserted whereby the fin is secured to the tube. These known methodsof attaching helical fins to tubes are unsatisfactory for variousreasons. Thus, the soldered constructions are relatively expensive tomanufacture and entail considerable loss of soldering material whichadheres to nortions of the tube and fin where it is not needed. Thegrooving method of fin attachment, although satisfactory for certaintypes of work, cannot be used with success when the tube walls are thin,because the grooving considerably weakens the tube.

The present invention has for its object, the provision of new andimproved apparatus for securing a helical fin to a tube and a new andimproved -finned tube produced by this apparatus.

According to the present invention, the outer surface of the tube isfirst roughened to produce a plurality of teeth, knurl marks or othersurface extensions or irregularities which preferably form ridge-likeprotrusions extending in a direction generally longitudinally of thetube. The ribbon or fin is then tightly wound edgewise on the tube andits inner edge is pressed against the tube surface with sufficient forceto cause the pro-' trusions or knurl marks on the tube surface to embedthemselves into the inner edge surface of the fin. When so wound, it isfound that the engagement of the tube surface protrusions or knurl markswith the fin edge is suflicient to effectively prevent the slipping ofthe fin around the tube surface and a highly efiicient finned tubeconstruction is thereby produced.

It has been discovered that a highly efiBQtive heat conductive bond maybe secured between a tube and a helical fin if the fin be merely tightlycoiled edgewise about the tube. The present invention provides a meansfor preventing such tightly wrapped fin from unwinding or otherwiseloosening after it has been coiled on the tube, and this without the useof solder or similar expedients. and without embedding the fin in thetube surface or otherwise weakening the tube structure.

A feature of the present invention comprises winding the metallic fin onthe tube in such a manner that the winding operation serves to stretchor extend a portion of the fin metal adjacent theouter edge thereofwhile the portion of the fin metal adjacent the inner edge thereof,against the tube surface, is compressed, but not beyond its elasticlimit.- With this procedure, the inner elastically compressed portion ofthe force on the tube surface and so maintains the fin firmly in placeon the tube, this expansive force being exerted between the tube surfaceand the set outer portion of the fin metal which-has been stretchedbeyond its elastic limit and so maintains the coiled formation of thefin in spite of the expansive force.

The helical fin may be precoiled before attachment to the tube or thecoiling and attachment of the fin may be effected in a single continuousoperation. Also, the surface protrusions or knurl marks may be formed onthe tube before or simultaneously with the winding operation.

The invention will be best understood by reference to the accompanyingdrawings in which certain embodiments thereof have been illustrated.Inthe drawings:

Fig. 1 is an elevation of a section of knurled tubing to which a portionof a precoiled helical fin has been attached in accordance with the in-40 vention;

Fig. 2 is a perspective view of a tube showing one method of formingsurface protrusions or knurl marks thereon;

Fig. 3 is an end elevation of a finned tube in the course ofconstruction in accordance with one embodiment of the invention;

Fig. 4 is a sectional view, taken along the line 4-4 of Fig. 3 andviewed in the direction of the arrows;

. Fig. 5 is a sectional view, taken along the line 5-5 of Fig. 3 andviewed in the direction of the arrows; and

Fig. 6 is an end elevationof a finned tube in the beyond its elasticlimit 15 fin exerts a considerable 2o course of construction inaccordance with another embodiment of the invention.

In a preferred embodiment of the invention, as best shown in Figs. 3 and4, a metallic tube 5 is simultaneously provided with externallongitudinally extending protrusions or knurl marks 6 and a precoiledmetallic fin or ribbon 7 is attached thereto. Various means may beprovided for effecting these operations. In the disclosed embodiment,the tube 5 is continuously rotated axially on a lathe or other suitabledevice and a ribbon lead and tension roll 8 and a knurling roll 9 areslowly moved in unison axially along the tube in the direction indicatedby the arrows in Figs. 4 and 5.

In order that the tube may be carried in the desired position withregard to the rolls 8 and 9, a tube supported roll 19 is provided andthe rolls 8, 9 and 19 are preferably. spaced about the tube 5 at anglesof substantially 120 C., as shown in Fig. 3. The roll 9 may be journaledin a block 20, slidably supported in a frame 21 and the rolls 9 and 19may be journaled in similar blocks 22 and 23 slidably supported in theframe 24. The roll-carrying blocks 20, 22 and 23 maybe respectivelymovable by screw means indicated at 25, 26 and 27 to facilitate theinsertion of the tube 5 between the rolls. The frames 21 and 24 may bemoved in unison along the tube by any suitable means. A fin guide 28 ispreferably provided, and

' as shown, may be fixed to the frame 24. The end of the guide 28 isdisposed adjacent the tube 5 between the knurlingv roll 9 and the leadand tensionroll 8, and embraces the fin '7 in a slot 29.

The lead and tension roll 8 is preferably constructed to provide aperipheral groove 13 for the reception of the fin 7, at least a portion.of this peripheral groove being disposed at an angle to the .normalplane of the fin. As best shown in Fig. 4, this may be accomplished byforming the roll 8 in two parts 31 and 32 having parallel complementaryfrusto conical end surfaces. These surfaces are sufficiently separatedto accommodate the fin '7 therebetween. but the angular disposition ofthe fin groove results in a firm frictional engagement between the fin 7and the roll 8 whereby the inner edge of the fin is tightly pressed onthe tube surface and the fin is maintained under sufilcient tension toensure tight winding on the tube.

The tube supporting roll 19 may comprise two spaced parts forming aperipheral groove 33 therebetween, as shown in Fig. 5. The groove 33' inthis roll merely acts to accommodate the fin 7 so that the peripheralsurfaces of the roll may engage and support the tube 5.

The knuriing roll 9 is provided on its peripheral surface with aplurality of teeth or serrations 14 which extend substantially atright-angles to the plane of rotation of this roll. The roll 9 is firmlypressed against the surface of the tube 5 and thus, as the tube rotates,forms surface protrusions or knurl marks 6 on the tube. The knurl marksor protrusions 6 are generally ridge-like in character and extend in adirection generally longitudinally of the tube. The knurling roll 9 ispreferably of suflicient widthso that in its movement along the tube 5,it forms knurl marks or protrusions along substantially the entiresurface of the tube, although it is suflicient for the purposes of theinvention that the knurl marks cover the path of the fin '7.

As shown in Figs. 1, 3, 4 and 5, the fin 7 used may be preformed to acoil having an inner diamnoea'see and the slot 29 of the guide 28-, thefin attaching operation is initiated by rotating the tube 5, andsimultaneously advancing the rolls 8, 9 and 19 along the tube. Theknurling roll '9 first engages the tube surface and forms the knurlmarks or surface protrusions 6 thereon, and as the rotation of the tubecontinues, the lead rol1'8 tightlywinds the fin '7 on the previouslyknurled tube surface and presses the inner edge of the fin against thissurface with sufficient force to cause the protrusions 0r knurl marks 6to-embed themselves in the inner edge of the fin '7. This penetration ofthe surface protrusions or knurl marks 6 into the fin edge prevents theslipping, of-the r fin 7 around the tube 5 and so maintainsthe fintightly wound on the tube. The tight winding of the fin '7 and theexplained penetration of the protrusions into the fin edge preventsmovement of the fin longitudinally along the tube.

The bending of the outer edge of the fin 7 as it passes through theangularly disposed groove 13 of the lead and tension roll 8 serves notonlyto maintain the fin under tension during winding and press the finedge against the knurl marks .6, but also acts to stretch the portion ofthe fin metal adjacent its outer edge beyond the elasticlimit of thismetal thereby setting the fin in its curved or wound position, while theinner portions of the fin are elastically compressed to an extent shortof the elastic limit of the fin metal. The wound fin, after beingsubjected to this treatment,

is permanently and tightly fixed to the tube, since the elasticallycompressed inner portion thereof tends to expand between the set outerportion and the tube surface. This stretching of the outer fin metalbeyond its elastic limit and an elastic compression of the inner finmetal during winding may be accomplished in other ways and in somecases, the relation between the fin width and the diameter to which itis bent in coiling it on the tube may be so chosen as to accomplish thedesired result. The present invention embraces this method as well asthat first described above.

It will be apparent'that the improved finned tube of the invention maybe formed by methods varying in some respects from that described above.Thus, the longitudinally extending protrusions or knurl marks 8 maybeformed on the tube 5 before the fin winding operation is effected. Asshown in Fig. 2, the smooth metallic tube 5 may be drawn through theopening in a die '15 having tooth or serration forming grooves 16 ontheinner surface thereof. These grooves 16 form longitudinally extendingridge-like protrusions or knurl marks 6 on the tube surface, similar tothe protrusions or knurlmarks 6 formed by the knurling roll 9 of Figs.3, 4 and 5.

After the protrusions or knurl marks 6' have been formed by the die 15,the precoiled fin 7 may be attached to the tube 5 by tightly winding thefin about the tube and pressing the. inner edge of the fin against theprotrusions 6' so that these protrusions bite into the fin edge. Thisoperation may be effected in the manner described above in connectionwith Figs. 3, 4 and 5, a lead and tension roll, similar to the roll 8,being employed for this purpose. The application of the fin 7 to a tube5 having previously formed surface protrusions orknurl marks 6 thereonis 9 and a tube supporting roll 19', carried by frames 21' and 24 whichmove longitudinally along the tube 5 as the winding operationprogresses. l'he rolls 8, 9 and 19' and the blocks and frames carryingthese rolls may be identical with the correspondingly designated partsof the winding apparatus of Figs. 3, 4 and 5 described above, and thisconstruction is clearly shown in Fig. 6. The frame 24' carries a ribbonguide block 17 having an aperture therein for the reception of the finor ribbon 7. As shown in the drawings, the ribbon carrying aperture inthe block 1'! guides the fin ribbon '1' in a tangential direction withrespect ato the tube 5. The lead and tension roll 8' frictionallyengages the ribbon 7' passing through the angularly disposed peripheralgroove therein and puts the proper tension on the rib-' bon so that itwill be adequately taut as it approaches the tube 5.

In operation, the tube 5 is rotated as indicated, the knurling roll 9'forms a plurality of knurl marks or surface protrusions extendingsubstantially longitudinally of thetubeand thereafter the fin ribbon 7'is tightly wound and pressed edgewise aganist the tube surface wherebythe protrusions or knurl marks on the tube'penetrate the inner edge ofthe fin and prevent subsequent movement of the fin on the tube, The

outer portion of the fin metal is at the same time stretched beyond itselastic limit in the angular groove of the lead and tension roll 8', andthe inner portion'of the fin metal is elastically compressed between theset outer fin metal and the conductive Joint without the of solder andwithout any weakening of the tube structure. The penetration of theridge-like protrusions on the tube into the inner edge of the finpermanently maintains the fin in its tightly. wound position. For thereasons given above, it is usually preferred to stretch the outer.portion of the fin metal beyond its elastic limit while the innerportion of the fin metal is compressed to a degree short of its elasticlimit to obtain the described resilient binding action, but thisresilient winding is not essential in certain embodiments of theinvention. When the resilient winding method of securing the fil r tothe tube is'employed, the knurling of the tube surface prior to theapplication of the fin may in certain cases be dispensed with, althoughit is generally preferred to attach the fin either by the lmurlingmethod alone or by a combination of knurling the tube surface andresiliently compressing the inner portion of the tube metal. 1

In the appended claims, the terms -protrusions" and.kn'url marks" areused to denote any form of surface irregularities which produceextensions capable of at least partially embedding themselves into theedge surface of the fin.

1. In a finned tube construction, a metallic tube, a continuous metallicfin tightly wound edgewise on the tube and protrusions on the surface ofthe tube penetrating the fin along its inner edge for preventingunwinding of the fi n from the tube.

2. In afinned tube construction, a, metallic tube, a continuous metallicfin tightly wound hellcally on the tube with one edgecontinuouslyengaging the tube surface and a plurality of knurl marks onthe tube presenting protrusions extending substantially longitudinallyof the tube and penetrating the fin along its inner edge for preventingmovement of the wound fin on the tube.

3. In a finned tube construction, a metallic tube, a continuous metallicfin tightly wound helically on the tube with one edge engaging the tubesurface and a plurality of knurl marks on the tube presenting ridge-likeprotrusions extending substantially longitudinally of the tube andpenetrating the inner edge of the fin for preventing movement of thewound fin on the tube, said penetrating ridges constituting the" solemeans for attaching the fin to the tube.

EDWARD A. DEWALD.

